Method for placing at least one duct/communication cable below a road surface in an area

ABSTRACT

The present invention relates to a method for placing at least one duct/communication cable below a road surface in an area, said area comprising a first layer (L 1  and a second layer (L 2 ), said first layer (L 1 ) being a road layer, such as asphalt or concrete, and said second layer (L 2 ) being a bearing layer for said first layer (L 1 ) and being located below said first layer (L 1 ), said method comprising the steps of: cutting a micro trench in said area through said first layer (L 1 ) into said second layer (L 2 ); placing at least one duct/communication cable in said micro trench so that said at least one duct/communication cable is placed below said first layer (L 1 ); and filling said micro trench so as to restore said road surface.

TECHNICAL FIELD

The present invention relates to method for placing at least oneduct/communication cable below a road surface in an area. Morespecifically, the invention relates to a method according to claim 1.

BACKGROUND OF THE INVENTION

The expansion of fibre optic networks for communication in residentialareas is often hampered by the high cost of excavation and restorationof the road layer, such as asphalt or concrete. A typical residentialconnection may cost approximately EUR 3 000 plus VAT, and hence manyhomeowners are reluctant to make such an investment. This in turn meansthat the connection rate for houses is low when a residential area isbuilt, which further increases the cost of connecting. The reason forthis is that the cost for the backbone is more or less independent ofthe connection rate, and a low connection rate means that fewer houseswill have to bear the total cost for the backbone.

An alternative, to provide house connections through green open spacesat the back of houses is in most cases not possible. Certainly, thiswould make the costs considerably lower as it may even be possible toplough down channelling tubing/ducts for fibre cables but this ofteninvolves crossing gardens in the homes of people not wanting to connect.There is also the question of flowerbeds, bushes and trees, which can becostly to replace/restored. Finally, it would probably be an enormoustask to arrange permission from all the homeowners affected if thismethod should be employed.

A technique for installing fibre is described in document L.40 producedby the International Telecommunication Union (ITU-T Recommendation L.49,2003). Document L.40 describes a micro trench installation technique forfibre cables.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method which fully orin part solves the problems of prior art solutions. Another object ofthe present invention is to provide a method for placing at least oneduct/cable (e.g. communication cable) below a road surface in an area ina way that reduces the cost for fibre installation compared to prior artmethods. Yet another object of the present invention is to provide analternative method for placing at least one duct/communication cablebelow a road surface in an area.

The above mentioned objects are achieved by a method for placing atleast one duct/communication cable below a road surface in an areaaccording to the invention. Said area comprises a first layer and asecond layer, said first layer being a road layer, such as asphalt orconcrete, and said second layer being a bearing layer for said firstlayer and being located below said first layer, said method comprisingthe steps of:

-   -   cutting a micro trench in said area through said first layer        into said second layer;    -   placing at least one duct/communication cable in said micro        trench so that said at least one duct/communication cable is        placed below said first layer; and    -   filling said micro trench so as to restore said road surface.

Embodiments of the method above are defined in the appended dependentmethod claims.

With a method according to the present invention ducts/communicationcables are placed at safe depth. This means that the fibre optic networkwill be safe if the road surface is removed and/or replaced. Further,the invention provides a method with minimum damage made to roads whenplacing ducts/cables which reduces the cost for restoration of the same.

Other advantages and applications of the present invention will beapparent from the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to clarify and explain the presentinvention, in which:

FIG. 1 shows a flow chart of a method according to the presentinvention;

FIG. 2 shows a flow chart of an embodiment of a method according to theinvention;

FIGS. 3 a and 3 b schematically shows a cross section of a roadway areawith a micro trench according to the invention;

FIG. 4 schematically shows the cross section in FIG. 3, wherein themicro trench is filled with filling material such as sand and sealedwith two sealing layers;

FIG. 5 shows a typical layout of a FTTH network;

FIG. 6 shows how to saw branches to individual homes from a main microtrench;

FIG. 7 shows branching to individual homes if boring is used instead ofsawing;

FIG. 8 shows a sawing machine according to an embodiment of theinvention with its sawing blade/disc cutter and a stabilizing devicestabilizing device for placing ducts/cables immediately behind thesawing blade;

FIG. 9 shows an embodiment of the sawing machine where the stabilizingdevice is adapted for placing a plurality of ducts/cables at the sametime while maintaining the order of the ducts/cables in the microtrench;

FIG. 10 shows in detail where to cut the top duct so that it will belong enough to reach its final destination;

FIGS. 11-13 shows further embodiments of the stabilizing device (thechannels are only illustrated in FIGS. 11-13 and should therefore not beseen as true representations).

DETAILED DESCRIPTION OF THE INVENTION

To achieve the above mentioned objects a method for placing at least oneduct/communication cable below a road surface in an area is provided bythe inventors.

The area comprises a first layer L1 and a second layer L2. The firstlayer L1 is a road layer, such as asphalt or concrete, and the secondlayer L2 is a bearing layer for the first layer L1 and is located belowthe first layer L1.

With reference to FIG. 1, which shows a flow chart of a method accordingto the present invention, the method for placing at least oneduct/communication cable below a road surface in the area comprises thesteps of:

-   -   cutting a micro trench in the area through the first layer L1        into the second layer L2;    -   placing at least one duct/communication cable in the micro        trench so that the at least one duct/communication cable is        placed below the first layer L1; and    -   filling the micro trench so as to restore the road surface.

FIGS. 3 a and 3 b schematically shows a cross section of an area inwhich a duct is placed in a micro trench. The area in FIGS. 3 a and 3 bis a three dimensional region of a typical roadway area, wherein thearea comprises a first layer L1 being a road layer such as asphalt orconcrete, and a second layer L2 being a bearing layer for the firstlayer L1 and usually consisting of macadam, sand and earth. The secondlayer L2 is naturally located below the first layer L1 as shown in FIG.3.

According to the invention the cutting step involves: cutting the microtrench through the first layer L1 into the second layer L2, which meansthat the micro trench is cut as shown in FIGS. 3 a and 3 b. The microtrench is cut so deep that at least one duct/communication cable isplaced in the micro trench below the first layer L1 (i.e. all installedducts/communication cables are placed below the first layer L1). Usingthe present method all ducts and cables for fibre optic networks can beplaced deep enough so that they are safe if the road layer L1 is removedand/or replaced, e.g. when repairing the road.

Thereafter, the at least one duct and/or a communication cable is placedin the micro trench. The duct is a duct arranged to hold “air-blownfibre” (so called EPFU) or fibre cables. The duct/s and/or thecommunication cable/s are placed in the micro trench so that they areentirely positioned below the first layer L1.

Finally, the micro trench is filled with a suitable filling material sothat the road surface is restored. The filling material is sand or anyother material with suitable properties. The micro trench is filled withthe filling material to a suitable level, and if needed the fillingmaterial is thereafter packed with a compactor that fits the width w ofthe micro trench.

Finally, the micro trench is sealed using a sealing material, such asbitumen, in order to get a water tight sealing. If a water tight sealingis not needed, patching may also be made with cold asphalt which is asimple and cheap method of restoration. A suitable amount of coldasphalt is simply poured and scraped into the micro trench, andthereafter compacted to a smooth and hard surface. Any excess asphaltcan then be collected and removed.

The filling step may according to a preferred embodiment of theinvention further involve the steps of:

-   -   sealing the micro trench flush to a bottom of the first layer L1        with a first sealing S1; and    -   sealing the micro trench flush to a surface of the first layer        L1 with a second sealing S2.

FIG. 4 shows the above described embodiment. The surface and the bottomof the first layer L1 are indicated in FIG. 4. In order to obtain asealed repair with high adhesion it is recommended to pour hot bitumenor bitumen mix when sealing the micro trench. However, other materialsuch as concrete or polymer modified asphalt will work.

The first sealing S1 is put down to seal the micro trench substantiallyflush with the bottom of the first layer L1 so that the micro trench canbe cleaned with a high-pressure washer to remove any residue of sandfrom the asphalt/concrete edges. After washing, the micro trench may bedried and pre-heated using a propane burner and finally, the microtrench is filled flush with the top surface of the first layer L1 usinga suitable sealant such as a hot crack sealant based on bitumen.

According to yet another embodiment of the invention, the micro trenchis sawn/cut with a disc cutter/sawing machine having a diamond coatedsawing disc. Such a diamond coated sawing disc can easily saw througheven the hardest materials, such as stone and concrete, and has provedvery useful in the present application since it provides exceptionallyclean cuts when cutting micro trenches. Prior art methods to cut microtrenches, such as using a sawing disc with tungsten carbide teeth,creates cracks in the edges of the micro trench that will make completesealing afterwards much harder and much more expensive compared theinvention.

The micro trench is preferably sawed/cut with a modified so-calledroad-saw (sawing machine) having a diamond coated sawing disc. Tofurther optimise the performance of the road saw in the presentapplication, the inventors have realised that one or more of thefollowing improvements are useful and should be considered asembodiments of the invention:

-   -   Change in rotational direction of the sawing disc to so-called        “up-cut” for improved transport of cuttings so as to keep the        trench clean which is important;    -   Modified cover for the sawing disc and a front outlet to        optimise the transport of cuttings and reduce spreading of dust        and leave the micro trench clean and ready for laying        ducts/cables;    -   Stabilizing device as shown in FIGS. 8 and 9 with one or more        guiding means for ducts/cables immediately after the sawing disc        so that micro trenching and placing of ducts/cables can be        carried out in one process. In case the stabilizing device has        guiding means for a plurality of ducts/cables, these guiding        means should be arranged so the outlets from the stabilizing        device are placed on top of each other in such a way that the        order of the ducts/cables from the inlet into the stabilizing        device and into the micro trench is preserved;    -   Trolley drawn by the road saw with holder for drums for        ducts/cables and warning tape with tracking wire; and    -   Servo to keep the sawing disc vertical on uneven surfaces, e.g.        when two wheels of the road-saw are on the pavement and two        wheels are on the road.

FIG. 8 shows an embodiment of the invention using a sawing machinecomprising a sawing disc arranged for up-cut. Up-cut is defined as therotating direction of the sawing disc in relation to the sawingdirection as shown by FIG. 8. All known sawing machines have theopposite rotating direction. By changing the rotating direction of thesawing machine to up-cut helps to remove the cut material from the microtrench, thereby providing “clean” micro trenches.

Further, the sawing machine comprises a stabilizing device arrangedimmediately behind the sawing disc, wherein the stabilizing device hasat least one guiding means, such as channels, for guiding the duct/cablewhen placed in the micro trench immediately after the sawing disc. If aplurality of ducts/cables is placed at the same time, the stabilizingdevice is arranged to be able to place the ducts/cables in preservedorder. This may be achieved by having individual channels for theducts/cables in the stabilizing device so that the order of theducts/cables will be maintained through the stabilizing device. Thereby,it is possible before the ducts/cables enter into the stabilizing deviceto identify which duct/cable will come out on top in the micro trenchand thereby making it possible to know which duct/cable to cut for eachfinal location, see FIG. 10.

Generally, the depth d of the micro trench should be larger than thedepth of the first layer d1 together with the height d2 of at least oneduct or at least one communication cable according to an embodiment ofthe invention, i.e. d>d1+d2 which means that the depth d of the microtrench is larger than the height of the first layer d1 plus the combinedheight of one ore more ducts and/or communication cables. As can bededuced from FIGS. 3 a, 3 b and 4, the above mentioned relation holds.

However, costs increase with increased depth d of the micro trench.Therefore, the micro trench should not be deeper than necessary. Normaldepth d of the micro trench can be around 400 mm, and unlike the width wof the micro trench, the depth d can often be adjusted continuouslywhile in operation when using a disc cutter. The cutter depth cantherefore be reduced gradually as the number of ducts laid in the microtrench is reduced.

Further, the micro trench should not be wider than necessary, since awider micro trench is more expensive than a narrow micro trench. On theother hand a narrower micro trench can make it more difficult to installthe ducts/cables, so there is an optimal width of the micro trench,since e.g. if the micro trench is too narrow, all ducts/cables will bepiled on top of each other so that the depth of the top duct/cable willbe too shallow.

From the above discussion, the inventors have through tests realisedthat suitable dimensions for a micro trench should have a depth dbetween 200-500 mm (and preferably 300-500 mm) and a width w between10-30 mm (and preferably 15-25 mm) according to an embodiment of theinvention for installation efficiency and low cost. Further, with thesedimensions minimum disruption of traffic is possible when placingducts/cables since traffic can pass over an open micro trench.

Furthermore, with reference to the flow chart in FIG. 2, according toanother embodiment of the invention, the method for placing at least oneduct/cable comprises the steps of:

-   -   scanning an area by means of a ground penetrating radar; and    -   identifying obstacles in the area using data generated by the        ground generated radar,    -   cutting a micro trench in the area through the first layer L1        into the second layer L2;    -   placing at least one duct/communication cable in the micro        trench so that the at least one duct/communication cable is        placed below the first layer (L1); and    -   filling the micro trench so as to restore the road surface.

It should be noted that the steps of scanning and identifying areperformed before the other steps in the method according to thisembodiment.

According to this embodiment, the area is scanned by means of a groundpenetrating radar device, such as a GEO-radar/scanner or any othersuitable equipment.

Thereafter, possible underground obstacles in the area, such as sewerpipes, electrical cables, construction structures, etc. are identifiedusing information generated by the ground penetrating radar device. Thescanning and identifying steps means that when performing the subsequentcutting step it may be avoided to accidentally cut/damage obstacles inthe area which may result in delay and extra cost in the micro trenchingprocess. After cutting a micro trench in the scanned area, at least oneduct and/or a communication cable is placed in the micro trench.Finally, the micro trench is filled with a suitable filling material sothat the road surface is restored.

The method according to the invention may also involve the step of:installing or blowing fibre or fibre cable in one or more ducts if ductswere placed in the micro trench.

It should also be noted that the method described above also maycomprise the step of: making one or more branching points connected tothe micro trench. Preferably, the branching points may be made by meansof a diamond coated core drill or a hand-held sawing machine with adiamond coated sawing chain or disc. As for this described embodimentthe method may also comprise the further step of: boring one or morechannels from the branching points to one or more houses usingcontrolled or guided boring. It is important that channels are boredbelow the first layer L1 in the second bearing layer L2. Ducts/cablesare thereafter installed in these channels when the drill is pulledback.

Different aspects concerning the layout of micro trenches, branchingpoints and channels, and strategies of cutting, branching, etc, inrelation to and incorporated in the present invention will be discussedin the following description.

Layout

FIG. 5 shows a typical logical structure of a Fibre To The Home (FTTH)network in a residential area, where “D” is a distribution node and “F”is a splicing point where larger fibre cables are spliced to smallerones (or in case of a PON network where optical splitters are placed).The network between a distribution node D and a splicing point F iscalled distribution network and the network between the splicing point Fand the individual homes is called access network. Both the ducts/cablesfor the distribution network and for the access network can be installedusing the method according to the present invention.

A residential area being constructed with FTTH is normally divided intoa number of smaller residential subareas. Somewhere in the residentialarea or outside of the residential area there must be a site whereoptical panels and electronics needed to form a so-called distributionnode D are housed. The distribution node D can be housed in an existingbuilding or in a small dedicated built building or in a large groundcabinet. Each distribution node D may contain electronics and opticalpanels for anywhere between a few hundred households up to severalthousand households. The size of the area to be built from a singledistribution node D can be adjusted within wide limits and dependsprimarily on practical considerations, such as space in the distributionnode D, difficulties with management of a large number of smallerdistribution nodes D, etc. This concept can also be adapted for anynumber of fibres per household.

There are two main types of FTTH networks: point-to-point-networks andpoint-to-multipoint networks. In a so-called point-to-point-network, thedistribution node D contains the other ends of all fibres that originatefrom the households in the residential area. If e.g. a residential areawith 500 households is being equipped with 2 fibres per house, therewill be 1000 incoming fibres to the distribution node D. Thedistribution node D should preferably have a central location in thearea being built as shown in FIG. 5.

The fibre structure of a point-to-multipoint-network or a so-calledPassive Optical Network (PON) is more or less the same. The differencebeing that the number of incoming fibres to the distribution node D inthis case equals the number of households divided by a factor (e.g. 8,16, 32, etc.). The examples in the continuing discussion are madeassuming that a point-to-point-network is being built. However,described methods also apply to a PON if only the distribution cablesare scaled accordingly.

Viewed from the distribution node D, distribution cables extend out tosplicing points F in manholes or cabinets. Distribution cables arenormally designed for the number of households in the area plus 10%spare so that in the future, newly built buildings easily can be addedto the network. In a point-to-point-network, if e.g. a splicing pointcovers an area with 22 houses and the requirement is two fibres perhouse, then 48 fibres from the distribution cable are needed. Fibresfrom the distribution cables are spliced in the splicing points F tofibres from the access cables. These access cables then extend to eachone of the houses being connected.

How many houses a splicing point F serves mainly depends on economicissues. If the covered area is too large, this will increase the averagelength of access cables to the houses, which increases costs. On theother hand, if the covered area is too small the cost for each housewill rise in relation to its share of splicing point F and distributioncable. Hence, there is an optimum size to the residential area where thecost is the lowest. The number of houses that would minimise the costdepends mainly on the topography of the residential area and how largethe plots of land are on which the houses are standing, but a rule ofthumb is that an optimum size is normally somewhere between 16 and 48houses from each splicing point F according to the invention.

If micro trenching is carried out using a disc cutter according to anembodiment of the invention, the splicing point F should be placedcentrally in each residential subarea, with e.g. around 22 houses. Thesplicing point F can be physically realised in a street cabinet or in amanhole by the roadside. Then, typically 10-12 ducts extend from theground cabinet or manhole each way along the road. Each of these ductsthen extends into each of the houses. Finally, access cables are blowninto each of these ducts.

Strategy when Cutting

Usually, residential areas have houses on both sides of a road, and thissituation can be tackled in one of two different ways: either microtrench in the roadside on both sides of the road and connect the housesto the closest micro trench, or micro trench on only one side of theroad or in the middle of the road and connect houses on both sides tothis micro trench.

However, to minimise the number of micro trenches across the road, startto micro trench to a boundary between two properties (houses) on theopposite side of the road according to an embodiment of the invention.Then place a duct/channelling tube in that micro trench to each one ofthe two properties. In this way, a micro trench across the road needonly be made for every second property on the opposite side of the road.Micro trenching across the road for every second property then this willbe a cheap and cost effective method.

Branching off a Main Trench

Branching off from a main micro trench (a main micro trench is definedas a micro trench along a road) can be carried out in a number of ways.The branches may be sawn either before as shown in FIG. 6 or after themain micro trench is sawn. Both methods are best done at about a 45°angle from the main micro trench in order to obtain a large radius curvefor the ducts/tubing. The branches may cross the location of the mainmicro trench or go “flush” with the main trench. When the main microtrench is sawed and the ducts/channelling tubes are laid it is easy toone by one route one of the uppermost tubes through each of the sawedbranches up to each residence, as shown in FIG. 10 and to the right inFIG. 6.

An alternative method of branching is to first bore a hole at eachbranching point with a suitably sized core drill. The main micro trenchcan then be cut along all these holes in the same maimer as describedabove as shown in FIG. 7. This method is suited both to making the houseconnections with a micro trench cut in the way described above as wellas making house connections with controlled boring.

An alternative method of branching is to first make a hole at eachbranching point. The holes may be made using a suitably sized core drill(for a round hole) or using a hand tool with a diamond cutting blade orchain (for a square hole). The main micro trench can then be cut alongall these holes in the same manner as described above and as shown inFIG. 7. This method is suited both to making the house connections witha micro trench cut in the way described above as well as making houseconnections with controlled boring. Controlled boring is sometimespreferred for making the house connections, because it avoids (e.g. goesunder) obstacles like fences, hedges, trees, etc. However, another pieceof expensive machinery (core drill) is needed at the installation site.

Sawing Machine and Stabilizing Device

It has been realized by the inventors that the placement/installation ofducts/cables should preferably be made before the sides of the trenchcollapses and before stones (or debris) and in particular stones largerthan the width of the trench are wedged into the sides of the trench andprevents the installation of the ducts/cables all the way down to thebottom of the trench. By achieving this time (and money) can be savedsince the installation can be performed without unnecessaryinterruptions.

Therefore, a sawing machine as already mentioned is arranged for sawingmicro trenches in an area. In this respect, the machine comprises a sawblade, preferable circular in shape, for sawing/cutting the microtrenches. The produced micro trenches are adapted for receivingducts/cables which means that the micro trenches have the properdimensions.

The machine also comprises a stabilizing device arranged for stabilizingthe walls of the micro trench when placing ducts/cables, and for thispurpose the stabilizing device is positioned immediately behind the sawblade in the micro trench, so that the walls are stabilized until theducts/cables have bee placed/installed by means of guiding means whichare also arranged on the stabilizing device.

For stabilizing the walls of the trenches, the stabilizing devicecomprises suitable stabilization elements such as proper side elementswhich are arranged to “hold up” the walls until the ducts/cables havebeen installed in the trenches. It is important that the stabilizingdevice is positioned immediately behind the saw blade so that thetrenches sawn by the saw blade are stabilized directly after they areproduced so that they do not collapse, or that debris or other dirt fallinto the trenches before the ducts/cables have been placed. Therefore, aclosest distance between the saw blade and the stabilizing device islarger than 0 mm but less than 10 mm according to an embodiment. Thedimension of the stabilizing device is dependent on the size of theducts/cables, the number of ducts to be placed at the same time, and thedepth for placement in the trench. However, the width of the stabilizingdevice should be slightly less then the width of the sawing blade.

Furthermore, for achieving controlled and automatic placement of theducts/cables the device has also guiding means which guides theducts/cables into the trench in a controlled and ordered manner. Thecombination of stabilization and guiding has proved to reduce cost andtime in an effective manner since the process of sawing and installingcan be performed at the same time. The guides are arranged on thestabilizing device and hence makes it possible to place the ducts/cablesinto the trench while the trench is stabilized by the device. Theducts/cables can therefore be placed with high precision into the trench(e.g. on the correct height in the trench) since the trench is “clean”as long as the trench is stabilized by the device.

The stabilizing device may be made of any suitable strong material sothat the trenches are stabilized. The material should preferably berigid, tough, hard and yet flexible so as to withstand stress duringoperation. The mounting of the stabilizing device to the sawing machineshould have an amount of flexibility to prevent damage if thestabilizing device is stuck in the trench. Steel or steel alloys aresuitable since they can be given the right properties by alloying withdifferent metals such as platinum and manganese. There is limited spacein the trench so the walls of the stabilizing device have to be thin aspossible so as to be able to accommodate the passing the ducts/cablesbut still have the properties mentioned above. Steel alloys in thehardness of about 400-700 Brinell have proved suitable for theseapplications. It has also been realised that the stabilizing device canbe made of moulded carbon fibre. Different parts of the stabilizingdevice can be cast separately and assembled into stabilizing deviceassembly.

According to an embodiment, the device has an inlet and an outlet forducts/cables, the inlet and outlet being connected to the guiding means.Preferably, the guiding means are channels through which theducts/cables are guided through the stabilizing device. When inoperation, the inlet is preferably above ground and vertically or closeto vertically arranged while the outlet is below ground in the trenchand horizontally or close to horizontally arranged in order to minimizewear and tear on the ducts/cables. Therefore, a minimum distance betweenthe outlet and the saw blade (at ground lever) is slightly longer thanthe recommended minimum bending radius for the ducts/cables to beinstalled. This normally translates to somewhere between 100 to 500 mmmeasured at ground level, but other distances are possible. Further, theinlet, outlet and guiding means may together be removably attached onthe stabilizing device e.g. in the form of a removable cassette. Byhaving a removable cassette for the guiding means, the installation timeshortens in some cases as the time consuming task of inserting manyducts/cables into their respective channels may be avoided

It has also been realized by the inventors that an operating depth forthe stabilizing device in the micro trench should be up to 50 mm lessthan an operating depth for the saw blade according to an embodiment.This difference in depth between the saw blade and the stabilizingdevice, when in operation, decides how quickly the ground level maychange (i.e. goes down). The saw blade must have sawed the trench deepenough so that the stabilizing device never touches the bottom of thetrench in order to avoid the possibility of the stabilizing devicesticking to the ground. This avoids unnecessary forces on thestabilizing device and possible breakage. This may happen when theground level suddenly becomes lower.

Moreover, according to yet another embodiment, the stabilizing deviceand the saw blade are arranged to be elevated and lowered independentlyof each other. This is advantages when for example the saw blade has tobe changed due to wear or when another type of saw blade is needed (e.g.one type for asphalt and another type for concrete). Further, thestabilizing device may have to be replaced which may easily be performedif the two parts can be lowered and elevated independently of eachother. Also, during shorter interruptions in the sawing operation thesawing blade is elevated, but the stabilizing device must remain in theground, since the need for stabilization of the trench still exists.However, the stabilizing device and the saw blade may further bearranged to together be elevated and lowered, e.g. when undergroundinfrastructure is encountered both parts can be elevated so as to avoiddamage.

The stabilizing device is preferably mounted separately on the sawingmachine by means of a number of movable axes for elevation and lowering.The movable axes may be powered by a dedicated engine for this specificpurpose. Further, the sawing machine may have on its left and rightsides (in the sawing direction) quick mount attachments means anddriving means for both the stabilizing device and the saw blade.Thereby, any of the left or right sides of the sawing machine can beused for sawing and placing ducts/cables which may be necessary due tohindering infrastructure, traffic situation in the areas, etc.

FIG. 9 shows an embodiment of a machine. The stabilizing device has afront part and a back part, wherein the front part is locatedimmediately behind the saw blade. It can also be seen that thestabilizing device has a section at the front part that has a shape thatis complementary to the shape of the saw blade which in this particularcase is circular. Thus, in case the section at the front part has aconcave circular shape with the same radius, or close to the sameradius, as the saw blade and is placed as close as possible and lessthan 10 mm away from the saw blade. The reason for this is that theunderground part of the stabilizing device must be arranged so close tothe saw blade such that it is virtually impossible for dirt, stones andother debris to fall to the bottom of the trench or wedge between thesides of the trench. The guiding means in this embodiment are guidingchannels inside the stabilizing device. The channels are illustratedwith dotted lines in the figures.

Further, the back part of the stabilizing device where the outlet isarranged may have different preferred shapes. One shape is substantiallyparallel to the complementary shape of the front section describedabove. Another shape is substantially opposite to the complementaryshape, and a third embodiment defines a shape for the back part which issubstantially diagonal from the base to the top of the back part in thebackwards direction. These embodiments are shown in FIGS. 11-13. It isfurther to be noted that the inlet, outlet and channels are arranged onthe back part of the stabilizing device in this embodiment. Thestabilizing device may also be axe shaped in cross section at frontpart.

Preferably, as mentioned above the stabilizing device has a maximumwidth in cross section that is equal to or slightly less than a widthfor the saw blade. The stabilizing device must be wide enough to haveroom for the ducts/cables to be installed, but small enough so that itcan be drawn along the sawed trench.

Another important aspect is that with the use of guiding means an orderof a plurality of ducts/cables is preserved when placed in the microtrench. This is very important when more than one duct is placed at thesame time. In one installation scenario, the duct/cable for a certainhouse is cut at a certain distance after the house. It is important thatthis duct/cable is one of the ducts/cables on top of the pile ofducts/cables in the trench, so that it can be easily found. Theduct/cable must be cut before the stabilizing device. Therefore it isimportant to know which one of all ducts/cables that enters thestabilizing device will come out on top in the trench. Moreover as thecolour of the duct/cable for a certain house is in many cases decidedbefore the sawing begins, the order of the ducts/cables must be arrangedso that the duct/cable with correct colour comes out on top, cut to thecorrect length, in the french when that particular house is passed.

A method which allows the placement of a plurality of ducts/cables atthe same time has a very high commercial value since the process ofplacement can be performed much faster than what has previously beenknow in the art. Therefore, according to this embodiment, thestabilizing device has a plurality of guiding means each guiding one ora few ducts/cables into the trench. For example, the device may comprisea plurality of channels so arranged that a know order is preserved,which means that an order of the ducts/cables out of the stabilizingdevice is known form the order of ducts/cables into the stabilizingdevice, hence the order into and out of the stabilizing device isrelated and known. This can e.g. be achieved by a one-to-one mappingbetween the inlet and the outlet of the device. The order of theducts/cables should be arranged in such a way that one of theducts/cables on top of the pile of ducts/cables in the trench is alwaysthe one to be routed to the next location. Therefore, a downmostduct/cable entering the inlet will be an uppermost duct/cable out fromthe outlet, and the uppermost duct/cable entering the inlet will be adownmost duct/cable out from the outlet. The branching micro trenchesmay be sawn before the main trench as shown in FIGS. 6 and 7 or thebranching micro trenches may be sawn after the main trench is sawn. Theparticular order in which the trenches are sawn may be decided toachieve the best flow during the installation. Each branching microtrench goes to a final location for one of the ducts/cables from themain micro trench. When the main trench is sawn and the ducts/cables areinstalled, the uppermost duct/cable is cut (before it enters thestabilizing device) at a certain distance beyond the location of therespective branching trench, so that that duct/cable can be lifted androuted to the final location for that duct/cable, see FIG. 10. If thecut is made correctly the length of the duct/cable will be sufficient sothat the duct/cable is long enough to reach the final location withoutsplicing. In this way the ducts/cables are one by one routed to eachpassed location through the branches.

Depending on the width of the trench and the size of theducts/communication cables there may be one or more ducts/communicationcables side by side as the uppermost ducts/communication cables in themain trench. It is important that the duct/communication cable next tobe routed to its final location is always one of the ones on top. Toachieve this is, when cutting the main trench and placing a number ofducts/communication cables, to cut one of the uppermostducts/communication cables, the one designated to this specificlocation, at a certain distance after passing the correspondingbranching trench, so that the cut duct/communication cable can be liftedand routed through that branching micro trench to its final location.The duct/communication cable should be cut at a certain minimum distanceafter passing the corresponding branching trench, so that, when liftedfrom the main trench and routed towards its final location, the lengthis sufficient to reach the final location without splicing.

If the stabilizing device (formerly known as “plough”) is designed withindividual channels for the ducts/cables or with individual channels,each with room for a few ducts/cables, it is easy to know whichduct/cable will be on top in the trench and thereby which duct/cableshould be cut before the stabilizing device. Example of such stabilizingdevice is shown in FIG. 9. The stabilizing device in this embodiment hasa duct/cable inlet and a duct/cable outlet which is connected to eachother by means of a plurality of channels as guiding means (illustratedwith dotted lines) for the ducts/cables. The underground outlet of thestabilizing device may in an embodiment comprise a “matrix” (or vector)part so arranged that the channels are arranged in a matrix with n rowand in columns, thereby in a controlled way horizontally and/orvertically separating the ducts/cables when placing them in the microtrench.

So in summery, the above described embodiment of the method involves;one after the other, cutting one of the uppermost ducts/communicationcables, which one is designated to a certain location, at a certainminimum distance after each branch and thereafter lifting thisduct/communication cable from the main trench and routing it to itsfinal location through the branch.

The machine may further comprise at least one drum arranged for holdingthe ducts/communication cables before placing them into the micro trenchvia the stabilizing device. In this way easy access to theducts/communication cables is achieved.

Further, the machine may also comprises other suitable means, such as:one or more engine means for powering the saw blade and the stabilizingdevice and/or for driving means (e.g. drive train and wheels),communication means for wireless communication with e.g. a remote serverunit, processing means, memory means, sensors, GPS means, vehicle means,display means for displaying information such as graphics, data basemeans, reading means for reading mechanical coding means on the sawblade, immobilizer, etc.

Regarding the driving of the saw blade and/or the stabilizing devicethis can e.g. be performed by means of direct mechanical driving,hydraulic driving and electric driving. The mechanical driving gives thehighest power transmission ration while the electrical driving gives thelowest, so the former is preferred if high power is needed which oftenis the case.

Finally, it should be understood that the present invention is notlimited to the embodiments described above, but also relates to andincorporates all embodiments within the scope of the appendedindependent claims.

1. Method for placing at least one duct/communication cable below a roadsurface in an area, said area comprising a first layer (LI) and a secondlayer (L2), said first layer (LI) being a road layer, such as asphalt orconcrete, and said second layer (L2) being a bearing layer for saidfirst layer (LI) and being located below said first layer (LI), saidmethod comprising the steps of: cutting a micro trench in said areathrough said first layer (LI) into said second layer (L2); placing atleast one duct/communication cable in said micro trench so that said atleast one duct/communication cable is placed below said first layer(LI); and filling said micro trench so as to restore said road surface.2. Method according to claim 1, wherein said micro trench has a depthd>d1+d2, where d1 is a depth of said first layer (LI) and d2 is a heightof said at least one duct/communication cable.
 3. Method according toclaim 2, wherein said micro trench has a depth d between 200-500 mm anda width w between 10-30 mm.
 4. Method according to claim 1, wherein saidstep of filling involves: filling said micro trench with a fillingmaterial, such as sand.
 5. Method according to claim 1, wherein saidstep of filling further involves: sealing said micro trenchsubstantially flush to a bottom of said first layer (LI); and sealingsaid micro trench substantially flush to a surface of said first layer(LI).
 6. Method according to claim 5, wherein said micro trench issealed using one or more sealant in the group comprising: concrete, coldasphalt, bitumen and polymer modified asphalt.
 7. Method according toclaim 1, wherein said step of cutting involves: cutting said microtrench using a sawing machine.
 8. Method according to claim 7, whereinsaid sawing machine has a diamond coated saw blade.
 9. Method accordingto claim 7, wherein said sawing machine is arranged for up-cut. 10.Method according to claim 7, wherein said step of placing involves:placing said at least one duct/communication cable by means of astabilizing device positioned immediately behind said sawing machine.11. Method according to claim 10, wherein said stabilizing devicecomprises guiding means for guiding one or more of ducts/communicationcables into said micro trench.
 12. Method according to claim 11, whereinsaid method further comprises the steps of: arranging a plurality ofducts/communication cables in an order; placing said plurality ofducts/communication cables by means of guiding means such that saidorder is preserved when said plurality of ducts/cable are placed intosaid micro trench.
 13. Method according to claim 1, further comprisingthe step of: making one or more branching points connected to said microtrench.
 14. Method according to claim 13, wherein said one or morebranching points are bored by means of a core drill or a hand-heldsawing machine.
 15. Method according to claim 13, further comprising thestep of: boring one or more channels below said first layer (LI) fromsaid one or more branching points to one or more houses using controlledor guided boring.
 16. Method according to claim 1, further comprisingthe step of: installing or blowing fibre or fibre cable in said at leastone duct if said at least one duct is placed in said micro trench. 17.Method according to claim 1, further comprising the steps of: scanningsaid area by means of a ground penetrating radar; identifying obstaclesin said area using data generated by said ground generated radar;wherein said steps of scanning and identifying are performed before saidstep of cutting.